1. Field of the Invention
This invention relates to optical measurement systems, and more specifically, to a method and system for optical measurement using a resonator incorporating a non-uniform phase characteristic.
2. Description of the Related Art
Present-day wafer patterns, optical circuits, and other microstructures are manufactured with features smaller than the optical wavelength and are sometimes referred to as “sub-micron” or “nanometric” technologies. In the manufacturing process, it is necessary to inspect small structures, to determine whether or not they are manufactured to the tolerances demanded by functional requirements and to make necessary adjustments in the manufacturing process to avoid manufacturing defective components.
In addition to optical and electronic integrated circuits, optical devices such as diffraction gratings and photographic masks such as the one used in photolithography, as well as the photolithographic patterns have sub-micron feature sizes and also must be measured and/or inspected for proper manufacturing tolerances and to determine if errors are present in the photographic masks. Also, biological structures encountered in microbiological studies require detection and measurement of very small shapes having small height variation.
In order to measure the above-mentioned sub-micron structures, scanning microscopy techniques are typically used, including near-field optical microscopy. Resolving small features is not possible with typical far-field techniques, due to the interaction of the feature edges that each produce a diffracted beam. The diffracted field expands in a manner inversely proportional with the size of the structures and the diffracted beams from each of the features then interfere during the field propagation. The contribution from each of the discrete edges cannot be separated, causing the “diffraction limitations” well known in optical systems. The above-incorporated Patent Application and Patent disclose methodologies and systems for making optical measurements using resonators to enhance the resolution of the measurement beyond the limitations of traditional microscopy, by reducing the impact of diffraction on the measurement through introduction of a resonance in the measurement path.
However, even with resonator enhancement, diffraction still places a limitation on the resolution of an optical measurement system. Therefore, it would be desirable to further enhance the resolution of a resonator-enhanced optical measurement system.